Learning MVC Part 6: Generic Repository Pattern in MVC3 Application with Entity Framework


Introduction

Creating a Generic Repository pattern in an MVC3 application with Entity Framework is the last topic that we are about to cover in our journey of learning MVC.
The article will focus on Unit of Work Pattern and Repository Pattern, and shows how to perform CRUD operations in an MVC application when there could be a possibility of creating more than one repository class. To overcome this possibility and overhead, we make a Generic Repository class for all other repositories and implement a Unit of Work pattern to provide abstraction.

Our roadmap towards Learning MVC

Just to remind our full roadmap towards learning MVC,

Pre-requisites

There are few pre-requisites before we start with the article,
  1. We have running sample application that we created in fifth part of the article series.
  2. We have Entity Framework 4.1 package or DLL on our local file system.
  3. We understand how MVC application is created (follow second part of the series).

Why Generic Repository

We have already discussed what Repository Pattern is and why do we need Repository Pattern in our last article. We created a User Repository for performing CRUD operations, but think of the scenario where we need 10 such repositories.
Are we going to create these classes? Not good, it results in a lot of redundant code. So to overcome this situation we’ll create a Generic Repository class that will be called by a property to create a new repository thus we do not result in lot of classes and also escape redundant code too. Moreover we save a lot of time that could be wasted creating those classes.

Unit of Work Pattern

According to Martin Fowler Unit of Work Pattern “Maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems.”
From MSDN, The Unit of Work pattern isn’t necessarily something that you will explicitly build yourself, but the pattern shows up in almost every persistence tool. The ITransaction interface in NHibernate, the DataContextclass in LINQ to SQL, and the ObjectContext class in the Entity Framework are all examples of a Unit of Work. For that matter, the venerable DataSet can be used as a Unit of Work.
Other times, you may want to write your own application-specific Unit of Work interface or class that wraps the inner Unit of Work from your persistence tool. You may do this for a number of reasons. You might want to add application-specific logging, tracing, or error handling to transaction management. Perhaps you want to encapsulate the specifics of your persistence tooling from the rest of the application. You might want this extra encapsulation to make it easier to swap out persistence technologies later. Or you might want to promote testability in your system. Many of the built-in Unit of Work implementations from common persistence tools are difficult to deal with in automated unit testing scenarios.”
The Unit of Work class can have methods to mark entities as modified, newly created, or deleted. The Unit of Work will also have methods to commit or roll back all of the changes as well.
The important responsibilities of Unit of Work are,
  • To manage transactions.
  • To order the database inserts, deletes, and updates.
  • To prevent duplicate updates. Inside a single usage of a Unit of Work object, different parts of the code may mark the same Invoice object as changed, but the Unit of Work class will only issue a single UPDATE command to the database.
The value of using a Unit of Work pattern is to free the rest of our code from these concerns so that you can otherwise concentrate on business logic.

Why use Unit of Work?

Again Martin Fowler statements, “When you’re pulling data in and out of a database, it’s important to keep track of what you’ve changed; otherwise, that data won’t be written back into the database. Similarly you have to insert new objects you create and remove any objects you delete.
You can change the database with each change to your object model, but this can lead to lots of very small database calls, which ends up being very slow. Furthermore it requires you to have a transaction open for the whole interaction, which is impractical if you have a business transaction that spans multiple requests. The situation is even worse if you need to keep track of the objects you’ve read so you can avoid inconsistent reads.
A Unit of Work keeps track and takes responsibility of everything you do during a business transaction that can affect the database. When you’re done, it figures out everything that needs to be done to alter the database as a result of your work.”
You see I don’t have to concentrate much on theory, we already have great definitions existing, all we needed is to stack them in a correct format.

Using the Unit of Work

One of the best ways to use the Unit of Work pattern is to allow disparate classes and services to take part in a single logical transaction. The key point here is that you want the disparate classes and services to remain ignorant of each other while being able to enlist in a single transaction. Traditionally, you’ve been able to do this by using transaction coordinators like MTS/COM+ or the newer System.Transactions namespace. Personally, I prefer using the Unit of Work pattern to allow unrelated classes and services to take part in a logical transaction because I think it makes the code more explicit, easier to understand, and simpler to unit test(From MSDN).

Creating a Generic Repository

Cut the Redundancy…
Step 1: Open up our existing MVC3 application created in Part5 in Visual Studio.
Step2: Right click Learning MVC project folder and create a folder named GenericRepository and add a class namedGenericRepository.cs to that folder.
The code of the GenericRepository.cs class is as follows:
using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Entity;
using System.Linq;
using System.Linq.Expressions;

namespace LearningMVC.GenericRepository
{
public class GenericRepository where TEntity : class
{
internal MVCEntities context;
internal DbSet dbSet;

public GenericRepository(MVCEntities context)
{
this.context = context;
this.dbSet = context.Set();
}

public virtual IEnumerable Get()
{
IQueryable query = dbSet;
return query.ToList();
}

public virtual TEntity GetByID(object id)
{
return dbSet.Find(id);
}

public virtual void Insert(TEntity entity)
{
dbSet.Add(entity);
}

public virtual void Delete(object id)
{
TEntity entityToDelete = dbSet.Find(id);
Delete(entityToDelete);
}

public virtual void Delete(TEntity entityToDelete)
{
if (context.Entry(entityToDelete).State == EntityState.Detached)
{
dbSet.Attach(entityToDelete);
}
dbSet.Remove(entityToDelete);
}

public virtual void Update(TEntity entityToUpdate)
{
dbSet.Attach(entityToUpdate);
context.Entry(entityToUpdate).State = EntityState.Modified;
}
}
}

We can see, we have created the generic methods and the class as well is generic, when instantiating this class we can pass any model on which the class will work as a repository and serve the purpose.
TEntity is any model/domain/entity class. MVCEntities is our DBContext as discussed in earlier parts.
Step 3: Implementing UnitOfWork: Create a folder named UnitOfWork under LearningMVC project, and add a class UnitOfWork.cs to that folder.
The code of the class is as follows:
using System;
using LearningMVC.GenericRepository;

namespace LearningMVC.UnitOfWork
{
public class UnitOfWork : IDisposable
{
private MVCEntities context = new MVCEntities();
private GenericRepository userRepository;

public GenericRepository UserRepository
{
get
{
if (this.userRepository == null)
this.userRepository = new GenericRepository(context);
return userRepository;
}
}

public void Save()
{
context.SaveChanges();
}

private bool disposed = false;

protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
context.Dispose();
}
}
this.disposed = true;
}

public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}
}

We see the class implements IDisposable interface for objects of this class to be disposed.
We create object of DBContext in this class, note that earlier it was used to be passed in Repository class from a controller.
Now it’s time to create our User Repository. We see in the code itself that, simply a variable named userRepositoryis declared as private GenericRepository userRepository; of type GenericRepository serving User entity to TEntity template.
Then a property is created for the same userRepository variable in a very simplified manner,
public GenericRepository UserRepository
{
    get
    {
        if (this.userRepository == null)
            this.userRepository = new GenericRepository(context);
        return userRepository;
    }
}
I.e., mere 6-7 lines of code. Guess what? Our UserRepository is created.
(Taken from Google)
You see it was as simple as that, you can create as many repositories you want by just creating simple properties, and no need to create separate classes. And now you can complete the rest of the story by yourself, confused???? Yes it’sDBOperations, let’s do it.
Step 4: In MyController, declare a variable unitOfWork as:
private UnitOfWork.UnitOfWork unitOfWork = new UnitOfWork.UnitOfWork();
Now this unitOfWork instance of UnitOfWork class holds all th repository properties,if we press “.” After it, it will show the repositories.So we can choose any of the repositories created and perform CRUD operations on them.
E.g. our Index action:
public ActionResult Index()
{
    var userList = from user in unitOfWork.UserRepository.Get() select user;
    var users = new List();
    if (userList.Any())
    {
        foreach (var user in userList)
        {
            users.Add(new LearningMVC.Models.UserList() { UserId = user.UserId, 
              Address = user.Address, Company = user.Company, 
              FirstName = user.FirstName, LastName = user.LastName, 
              Designation = user.Designation, EMail = user.EMail, PhoneNo = user.PhoneNo });
        }
    }
    ViewBag.FirstName = "My First Name";
    ViewData["FirstName"] = "My First Name";
    if(TempData.Any())
    {
        var tempData = TempData["TempData Name"];
    }
    return View(users);
}
Here,
  • unitOfWork.UserRepository ­­> Accessing UserRepository.
  • unitOfWork.UserRepository.Get() -> Accessing Generic Get() method to get all users.
Earlier we used to have MyController constructor like:
public MyController()
{
    this.userRepository = new UserRepository(new MVCEntities());
}
Now, no need to write that constructor, in fact you can remove the UserRepository class and Interface we created in part 5 of Learning MVC.
I hope you can write the Actions for rest of the CRUD operations as well.

Details

public ActionResult Details(int id)
{
    var userDetails = unitOfWork.UserRepository.GetByID(id);
    var user = new LearningMVC.Models.UserList();
    if (userDetails != null)
    {
        user.UserId = userDetails.UserId;
        user.FirstName = userDetails.FirstName;
        user.LastName = userDetails.LastName;
        user.Address = userDetails.Address;
        user.PhoneNo = userDetails.PhoneNo;
        user.EMail = userDetails.EMail;
            user.Company = userDetails.Company;
        user.Designation = userDetails.Designation;
    }
    return View(user);
}
 
Create:
[HttpPost]
public ActionResult Create(LearningMVC.Models.UserList userDetails)
{
    try
    {
        var user = new User();
        if (userDetails != null)
        {
            user.UserId = userDetails.UserId;
            user.FirstName = userDetails.FirstName;
            user.LastName = userDetails.LastName;
            user.Address = userDetails.Address;
            user.PhoneNo = userDetails.PhoneNo;
            user.EMail = userDetails.EMail;
            user.Company = userDetails.Company;
            user.Designation = userDetails.Designation;
        }
        unitOfWork.UserRepository.Insert(user);
        unitOfWork.Save();
        return RedirectToAction("Index");
          }
    catch
    {
        return View();
    }
}
 
Edit:
public ActionResult Edit(int id)
{
    var userDetails = unitOfWork.UserRepository.GetByID(id);
    var user = new LearningMVC.Models.UserList();
    if (userDetails != null)
    {
        user.UserId = userDetails.UserId;
        user.FirstName = userDetails.FirstName;
        user.LastName = userDetails.LastName;
        user.Address = userDetails.Address;
        user.PhoneNo = userDetails.PhoneNo;
        user.EMail = userDetails.EMail;
        user.Company = userDetails.Company;
        user.Designation = userDetails.Designation;
      }
    return View(user);
}

[HttpPost]
public ActionResult Edit(int id, User userDetails)
{
TempData[TempData Name”] = Akhil”;

try
{
var user = unitOfWork.UserRepository.GetByID(id);
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
unitOfWork.UserRepository.Update(user);
unitOfWork.Save();
return RedirectToAction(Index”);
}

 
Delete:
public ActionResult Delete(int id)
{
    var user = new LearningMVC.Models.UserList();
    var userDetails = unitOfWork.UserRepository.GetByID(id);

if (userDetails != null)
{
user.FirstName = userDetails.FirstName;
user.LastName = userDetails.LastName;
user.Address = userDetails.Address;
user.PhoneNo = userDetails.PhoneNo;
user.EMail = userDetails.EMail;
user.Company = userDetails.Company;
user.Designation = userDetails.Designation;
}
return View(user);
}

[HttpPost]
public ActionResult Delete(int id, LearningMVC.Models.UserList userDetails)
{
try
{
var user = unitOfWork.UserRepository.GetByID(id);

if (user != null)
{
unitOfWork.UserRepository.Delete(id);
unitOfWork.Save();
}

return RedirectToAction(Index”);
}
catch
{
return View();
}
}

 
Note: Images are taken from Google images.

Conclusion

We now know how to make generic repositories too, and perform CRUD operations using it.

We have also learnt UnitOfWork pattern in detail. Now you are qualified and confident enough to apply these concepts in your enterprise applications. This was the last part of this MVC series, let me know if you feel to discuss any topic in particular or we can also start any other series as well.

Read more:

Other Series

My other series of articles:

For more informative articles visit my Blog.

For more technical articles you can reach out to CodeTeddy.

Learning MVC – Part 5:Repository Pattern in MVC3 Application with Entity Framework


Introduction

In our last four articles, we learnt almost everything about how to create an MVC application and how to communicate with database using the same application.
In the third part of learning MVC, we learnt communication between MVC application and database usingEntityFramework, so I am referring to the same context. In this article, I’ll focus on how to implement a Repository Pattern in the same MVC application, therefore moving ahead a step towards architectural approach of developing an enterprise application.

Our Roadmap

Just to remind you of our full roadmap towards learning MVC:

Pre-requisites

There are a few pre-requisites before we start with the article:
  1. We have running sample application that we created in the third part of the article series.
  2. We have EntityFramework 4.1 package or DLL on our local file system.
  3. We understand how the MVC application is created.

Repository Pattern

Very few authors explain the concept and jump directly over the practical implementation of the pattern. So, first let us understand what is repository pattern? Why should we use it?
In simple terms, a repository basically works as a mediator between our business logic layer and our data access layer of the application. Sometimes, it would be troublesome to expose the data access mechanism directly to business logic layer, it may result in redundant code for accessing data for similar entities or it may result in a code that is hard to test or understand. To overcome these kinds of issues, and to write an Interface driven and test driven code to access data, we use Repository Pattern. The repository makes queries to the data source for the data, thereafter maps the data from the data source to a business entity/domain object, finally and persists the changes in the business entity to the data source. According to MSDN, a repository separates the business logic from the interactions with the underlying data source or Web service. The separation between the data and business tiers has three benefits:
  • It centralizes the data logic or Web service access logic.
  • It provides a substitution point for the unit tests.
  • It provides a flexible architecture that can be adapted as the overall design of the application evolves.
When we use Entity Framework, as we did in our last application created, we were calling the Entity Framework class object in the controller class for accessing the entity classes. Now we can say that that system was somewhat a tightly coupled system. To overcome this situation, as we discussed, we’ll implement Repository Pattern.
In Repository, we write our whole business logic of CRUD operations with the help of Entity Framework classes, that will not only result in meaningful test driven code but will also reduce our controller code of accessing data.

Creating Repository

Creating Repository is not as tough at it sounds to be, once you implement this by your own, you’ll love it.
Step 1: Open up our existing MVC3 application in Visual Studio, that we created in the third part to interact with database with the help of Entity Framework.
Step 2: Create a folder named Repository and add an Interface to that folder named IUserRepository, this interface we derive from IDisposable type of interface.
We’ll declare methods for CRUD operations on User entity class over here, you can choose the names of the method as per your choice, but those should be easy to understand and follow.
Like I used in the below code of my interface:
using System;
using System.Collections.Generic;

namespace LearningMVC.Repository
{
public interface IUserRepository:IDisposable
{
IEnumerable GetUsers();
User GetUserByID(int userId);
void InsertUser(User user);
void DeleteUser(int userId);
void UpdateUser(User user);
void Save();
}
}

We can see each method name signifies particular CRUD operation on User entity.
User Entity is the same entity we generated in Model.tt class in Part3 of learning MVC, remember???????
Step 3: Extract a class from that interface and call it UserRepository. This UserRepository class will implement all the methods of that interface, but with the help of Entity Framework. Now here comes the use of our DBContextclass MVCEntities, we already have this class in our existing solution, so we don’t have to touch this class, simply, write our business logic in the interface methods implemented in UserRepository class:
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;

namespace LearningMVC.Repository
{
public class UserRepository:IUserRepository
{
private MVCEntities context;

public UserRepository(MVCEntities context)
{
this.context = context;
}

public IEnumerable GetUsers()
{
return context.Users.ToList();
}

public User GetUserByID(int userId)
{
return context.Users.Find(userId);
}

public void InsertUser(User user)
{
context.Users.Add(user);
}

public void DeleteUser(int userId)
{
User user = context.Users.Find(userId);
context.Users.Remove(user);
}

public void UpdateUser(User user)
{
context.Entry(user).State = EntityState.Modified;
}

public void Save()
{
context.SaveChanges();
}

private bool disposed = false;

protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
context.Dispose();
}
}
this.disposed = true;
}

public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}
}

And inside the solution:

Interface

Class

90% of the job is done now. Now the only thing left is to use this repository in our controller.
This is needless to explain how you’ll call repository inside the controller, as you now know how to treat our controller, but still let’s do it for once.
Step 4: Go to the controller, declare the IUserRepository reference, and in the constructor initialize the object withUserRepository class, passing MVCEntities to the constructor as parameter we defined in UserRepositoryclass:
#region Private member variables...
private IUserRepository userRepository; 
#endregion

#region Public Constructor…
/// <summary>
/// Public Controller to initialize User Repository
/// </summary>
public MyController()
{
this.userRepository = new UserRepository(new MVCEntities());
}
#endregion

In the solution, this will look like:

Step 5: Now for all the actions of the controller in which we were using Entity Framework context directly, we replace the calling logic by the created userRepository object, and call methods defined in repository class.
Like, in Index controller, where we show the list of users, we do:
var userList = from user in userRepository.GetUsers() select user;
            var users = new List();
            if (userList.Any())
            {
                foreach (var user in userList)
                {
                    users.Add(new LearningMVC.Models.UserList() 
                    { UserId = user.UserId, Address = user.Address, 
                    Company = user.Company, FirstName = user.FirstName, 
                    LastName = user.LastName, Designation = user.Designation, 
                    EMail = user.EMail, PhoneNo = user.PhoneNo });
                }
            }

We can see the earlier code used remained the same, only a layer has been introduced between Entity Framework data access layer and business logic, and the controller now only uses that abstracted layer to communicate with database.

Similarly for other Actions of the controller:

Details

Create

Edit

Delete

Step 6: Run the application, and we see the application running as it was earlier:

Now that’s party time.

Conclusion

We now know how to make repositories too, and perform CRUD operations using it.
Now we can visualize how useful the pattern is and how it solved our issues of tight coupling and resulted in an appropriate architecture.
As per MSDN, Use the Repository pattern to achieve one or more of the following objectives:
  • You want to maximize the amount of code that can be tested with automation and to isolate the data layer to support unit testing.
  • You access the data source from many locations and want to apply centrally managed, consistent access rules and logic.
  • You want to implement and centralize a caching strategy for the data source.
  • You want to improve the code’s maintainability and readability by separating business logic from data or service access logic.
  • You want to use business entities that are strongly typed so that you can identify problems at compile time instead of at run time.
  • You want to associate a behavior with the related data. For example, you want to calculate fields or enforce complex relationships or business rules between the data elements within an entity.
  • You want to apply a domain model to simplify complex business logic.
And I fully agree to it, but has our application made use of the pattern appropriately? What if there are 100s of Repositories that need to be created? What if we have 100s of entities? Do we create Repositories for all of them, resulting in a mess and code redundancy? The answer is a big NO. In my next and last article of the series, we’ll learn how to create a Generic Repository to serve the purpose of n number of Entities. The source code of this article and existing article, i.e., Part 3 along with database scripts has been attached. You can download and run the solution, and drop me a question in case you feel like it. I’ll be happy to answer.

Read more:

Other Series

My other series of articles:

For more informative articles visit my Blog.

For more technical articles you can reach out to CodeTeddy.

Learning MVC Part 4 : Creating MVC Application with EntityFramework Code First Approach


Introduction

In our first three articles, we learnt a lot about MVC, starting from definition to use, from creating an application to connecting the MVC application with database using different techniques.
In the very last part of the series, we learnt how to connect our MVC application with existing database using Entity Framework.
This article will focus on connecting our MVC application with database using CodeFirst approach, i.e., one of the features Microsoft’s Entity Framework provides.

Our Roadmap

Just to remind our full roadmap towards learning MVC:
 

Pre-requisites

There are few pre-requisites before we start with the article:
  1. We have the running sample application that we created in the third part of the article series.
  2. We have EntityFramework 4.1 package or DLL on our local file system.
  3. We understand how MVC application is created.

Code-First Approach

To achieve a domain driven design, Entity Framework introduced EF 4.1 Code First. In the Code First approach, we focus on the domain design or entities/POCO classes first and create classes as per our model requirement. We do not have the database of the application, rather we create database automatically from code after defining our domain. The database created perfectly matches with the domain we design, so we have to be very conscious and keen in designing our domain model. It feels exciting to see database created on the fly with the help of our entities and XML configuration, without even opening database server.
No matter, you are not an expert in database, if you are a C# developer, just focus on your model/class creation.EntityFramework will take headache of creating and managing database for you.

Procedure

Step 1: Open the MVC application that we created in Learning MVC-Part3 in your Visual Studio.
We can clearly see and remember what we used to connect our MVC application to database with the help of entity framework, yes it was edmx class and our Model.tt classes generated from edmx classes.
Step 2: We don’t need the existing data-base, so you can delete the already created database for our part 3 application (if created).
Step 3: We don’t need edmx files now, so let’s clean our application, wipe out all these classes. Just deleteEFDataModel.edmxModel1.Context.tt and Model1.tt files. Now please do not run the application. It will give compile time errors, since we were using those classes ;-), Our solution will look like:
Our old solution had UserList class in Models folder, I have only changed the name of the class for differentiating it with previous application, and readability as was in the first part.
Step 4: As simple as that, just add a class to your solution, and name it MVCDBContext.cs as shown in the following image:
Step 5: Just add System.Data.Entity DLL as a reference to the solution if not already added.
Step 6: Use the namespace System.Data.Entity in our DBContext class, and inherit the added class fromDBContext class,
DbContext class: According to MSDN, DbContext class is conceptually similar to ObjectContext. To define, theObjectContext class is the part of the core EF API in the Microsoft .NET Framework 4 and this is our hero class that allows us to perform queries, change tracking and update the database using the strongly typed classes that represent our model (entity class). The DbContext is a wrapper around ObjectContext that exposes the most commonly used features of ObjectContext as well as provides some simpler “shortcuts” to tasks that are frequently used but complicated to code directly with ObjectContext. Simplfied alternative to ObjectContext and is the primary object for interacting with a database using a specific model.
Step 7: Add a DBSet property to the DbContext class that we created:
public DbSet Users { get; set; }
User, defined in angular brackets, is the model that we created in Models folder, so our MVCDBContext class looks like:
using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Web;
using LearningMVC.Models;

namespace LearningMVC
{
public class MVCDBContext : DbContext
{
public DbSet Users { get; set; }
}
}

That’s it, our 90% work is done?
DbSet property: It is a simplified alternative to ObjectSet and is used to perform CRUD operations against a specific type from the model.
By default, the name of the DbContext class will be the name our database that will automatically be created, so be wise to select the name of context class, else it could be handled in web.config as well.
The name of model will be the name of Table in database and properties of model will be the columns of the table.

Our Heroes

Both DbContext and DbSet are our super heroes, in creating and dealing with database operations, and make us far abstracted, providing ease of use to us.
When we are working with DbContext, we are in real working with entity sets. DbSet represents a typed entity set that is used to perform create, read, update, and delete operations. We are not creating DbSet objects and using them indepedently. DbSet can be only used with DbContext.
Step 8: Define a connection string in web.config file, you can remove previously defined connection string, the new connection string will somewhat look like:
The name of the connection string will be the name of the DbContect that we defined, i.e., MVCDbContext.
Step 9: Now, we just have to modify the access method in controllers, earlier, when we created application in third part, we were accessing the context class from the modelcontext class that was generated from edmx file. Edmx file was added having reference to already created database.
But now the case is different, we don’t have a database now, we’ll access the table and columns using ourMVCDBContext class in controllers, so just change the following line of code used in Actions of earlier application:
var dbContext = new MVCEntities() ;
to
var dbContext = new MVCDBContext();
Job done. 
Just Hit F5, and you’ll see:
How does the application run, where is the database??? Dude, go back to your database server, and check for database:
We see our database is created, with the name MVCDB, that’s the magic of EntityFramework. Now we can perform all the CRUD operations on this database, using our application. Just create a new user.
In database we see, user created.
By default, integer property with ID in its name of model will be the primary key in the database, in our caseUserId, or you can define the primary key in the model too.

Conclusion

Now we know how to play with EntityFramework to create database as per our domain model from our code, we have already moved ahead to advanced concepts of MVC and Entity Framework.
When we see the definition of DbContext, it uses the terms Repository Pattern and Unit of Work Pattern. We’ll discuss these more in detail in my next article.

Read more:

Other Series

My other series of articles:

For more informative articles visit my Blog.

For more technical articles you can reach out to CodeTeddy.

ASP.Net MVC Interview Questions and Answers


Introduction:
My this article on Interview Questions and Answers of MVC basically covers most of the MVC 2, MVC3 and MVC4 topics that are more likely to be asked in job interviews/tests/exams.
The sole purpose of this article is to sum up important questions and answers that can be used by developers to brush-up all about MVC before they take any interview of the same kind.
What is MVC?
MVC is a framework pattern that splits an application’s implementation logic into
three component roles: models, views, and controllers.
  • Model: The business entity on which the overall application operates. Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be encapsulated by the Model.
  • View: The user interface that renders the Model into a form of interaction.
  • Controller: Handles a request from a View and updates the Model that results in a change of the Model’s state.
To implement MVC in .NET we need mainly three classes (View, Controller and the Model).
Explain MVC Architecture?
 
The architecture is self explanatory. The browser (as usual) sends a request to IIS, IIS searches for the route defined in MVC application and passes the request to the controller as per route, the controller communicates with the model and passes the populated model (entity) to View (front end), Views are populated with model properties, and are rendered on the browser, passing the response to browser through IIS via controllers which invoked the particular View.

What are the new features of MVC2?
ASP.NET MVC 2 was released in March 2010. Its main features are:
  1.       Introduction of UI helpers with automatic scaffolding with customizable templates.
  2.       Attribute-based model validation on both client and server.
  3.        Strongly typed HTML helpers.
  4.        Improved Visual Studio tooling
  5.       There were also lots of API enhancements and “pro” features, based on feedback from developers building a variety of applications on ASP.NET MVC 1, such as:

  •   Support for partitioning large applications into areas.
  •   Asynchronous controllers support.
  •   Support for rendering subsections of a page/site using Html.RenderAction.
  •   Lots of new helper functions, utilities, and API enhancements

What are the new features of MVC3?

ASP.NET MVC 3 shipped just 10 months after MVC 2 in Jan 2011.Some of the top features in MVC 3 included:
  •        The Razor view engine.
  •        Support for .NET 4 Data Annotations.
  •        Improved model validation
  •        Greater control and flexibility with support for dependency resolution and global action filters.
  •        Better JavaScript support with unobtrusive JavaScript, jQuery Validation, and JSON binding.
  •        Use of NuGet to deliver software and manage dependencies throughout the platform.

What are the new features of MVC4?
Following are the top features of MVC4:
  •       ASP.NET Web API.
  •       Enhancements to default project templates.
  •       Mobile project template using jQuery Mobile.
  •       Display Modes.
  •       Task support for Asynchronous Controllers.
  •       Bundling and minification.

Explain “page lifecycle” of an ASP.NET MVC?
Following process are performed by ASP.Net MVC page:
  1.  App initialization
  2.  Routing
  3.  Instantiate and execute controller
  4.  Locate and invoke controller action
  5.  Instantiate and render view
Advantages of MVC Framework?
  1.  Provides a clean separation of concerns between UI (Presentation layer), model (Transfer objects/Domain Objects/Entities) and Business Logic (Controller).
  2.  Easy to UNIT Test.
  3.  Improved reusability of views/model. One can have multiple views which can point tosame model and vice versa.
  4.  Improved structuring of the code.
What do you mean by Separation of Concerns?
As per Wikipedia ‘the process of breaking a computer program into distinct features that overlap in functionality as little as possible’. MVC design pattern aims to separate content from presentation and data-processing from content.
Where do we see Separation of Concerns in MVC?
Between the data-processing (Model) and the rest of the application.
When we talk about Views and Controllers, their ownership itself explains separation. The views are just the presentation form of an application, it does not have to know specifically about the requests coming from controller. The Model is independent of View and Controllers, it only holds business entities that can be passed to any View by the controller as required for exposing them to the end user. The controller is independent of Views and Models, its sole purpose is to handle requests and pass it on as per the routes defined and as per the need of rendering views. Thus our business entities (model), business logic (controllers) and presentation logic (views) lie in logical/physical layers independent of each other.
What is Razor View Engine?
Razor is the first major update to render HTML in MVC3. Razor was designed specifically as a view engine syntax. It has one main focus: codefocused templating for HTML generation. Here’s how that same markup would be generated using Razor:
@model MvcMusicStore.Models.Genre
@{ViewBag.Title = “Browse Albums”;}
<div class=”genre”>
<h3><em>@Model.Name</em> Albums</h3>
<ul id=”album-list”>
@foreach (var album in Model.Albums)
{
<li>
<a href=”@Url.Action(“Details”, new { id = album.AlbumId })”>
<img alt=”@album.Title src=”@album.AlbumArtUrl />
<span>@album.Title</span>
</a>
</li>
}
</ul>
</div>
The Razor syntax is easier to type, and easier to read. Razor doesn’t have the XML-like heavy syntax.
of the Web Forms view engine.
What is Unobtrusive JavaScript?
Unobtrusive JavaScript is a general term that conveys a general philosophy, similar to the term
REST (Representational State Transfer). The high-level description is that unobtrusive JavaScript doesn’t intermix JavaScript code in your page markup. For example, rather than hooking in via event attributes like onclick and onsubmit, the unobtrusive JavaScript attaches to elements by their ID or class, often based on the presence of other attributes (such as HTML5 data- attributes).
It’s got semantic meaning, and all of it — the tag structure, element attributes, and so on — should have a precise meaning. Strewing JavaScript gunk across the page to facilitate interaction (I’m looking at you, __doPostBack!) harms the content of the document.
What is JSON Binding?
MVC 3 included JavaScript Object Notation (JSON) binding support via the new
JsonValueProviderFactory, enabling the action methods to accept and model-bind data in JSON format. This is especially useful in advanced Ajax scenarios like client templates and data binding that need to post data back to the server.
What is Dependency Resolution?
MVC 3 introduced a new concept called a dependency resolver, which greatly simplified the use of dependency injection in your applications. This made it easier to decouple application components, making them more configurable and easier to test.
Support was added for the following scenarios:
  •       Controllers (registering and injecting controller factories, injecting controllers)
  •       Views (registering and injecting view engines, injecting dependencies into view pages)
  •       Action fi lters (locating and injecting fi lters)
  •       Model binders (registering and injecting)
  •       Model validation providers (registering and injecting)
  •       Model metadata providers (registering and injecting)
  •       Value providers (registering and injecting)

What are Display Modes in MVC4?
Display modes use a convention-based approach to allow selecting different views based on the browser making the request. The default view engine fi rst looks for views with names ending with .Mobile.cshtml when the browser’s user agent indicates a known mobile device. For example, if we have a generic view titled Index.cshtml and a mobile view titled Index.Mobile.cshtml, MVC 4 will automatically use the mobile view when viewed in a mobile browser.
Additionally, we can register your own custom device modes that will be based on your own custom criteria — all in just one code statement. For example, to register a WinPhone device mode that would serve views ending with .WinPhone.cshtml to Windows Phone devices, you’d use the following code in the Application_Start method of your Global.asax:
DisplayModeProvider.Instance.Modes.Insert(0, new DefaultDisplayMode(“WinPhone”)
{
ContextCondition = (context => context.GetOverriddenUserAgent().IndexOf
(“Windows Phone OS”, StringComparison.OrdinalIgnoreCase) >= 0)
});
What is AuthConfig.cs in MVC4?
AuthConfig.cs  is used to configure security settings, including sites for OAuth login.
 What is BundleConfig.cs in MVC4?
 BundleConfig.cs in MVC4 is used to register bundles used by the bundling and minification
 system. Several bundles are added by default, including jQuery, jQueryUI, jQuery  validation, Modernizr, and default CSS references.
 What is FilterConfig.cs in MVC4?
 This is used to register global MVC filters. The only filter registered by default is the    HandleErrorAttribute, but this is a great place to put other filter registrations.
 What is  RouteConfig.cs in MVC4?
 RouteConfig.cs holds the granddaddy of the MVC config statements, Route configuration.
 What is WebApiConfig.cs in MVC4?
 Used to register Web API routes, as well as set any additional Web API configuration settings.
What’s new in adding controller in MVC4 application?
Previously(in MVC3 and MVC2), the Visual Studio Add Controller menu item only displayed when we right-clicked on the Controllers folder. However, the use of the Controllers folder was purely for organization. (MVC will recognize any class that implements the IController interface as a Controller, regardless of its location in your application.) The MVC 4 Visual Studio tooling has been modified to display the Add Controller menu item for any folder in your MVC project. This allows us to organize your controllers however you would like, perhaps separating them into logical groups or separating MVC and Web API controllers.
What are the software requirements of ASP.NET MVC4 application?
MVC 4 runs on the following Windows client operating systems:
  •     Windows XP
  •     Windows Vista
  •     Windows 7
  •     Windows 8

It runs on the following server operating systems:
  •     Windows Server 2003
  •     Windows Server 2008
  •     Windows Server 2008 R2

MVC 4 development tooling is included with Visual Studio 2012 and can be installed on Visual
Studio 2010 SP1/Visual Web Developer 2010 Express SP1.
What are the various types of Application Templates used to create an MVC application?
The various templates are as follows,
1. The Internet Application template: This contains the beginnings of an MVC web
application — enough so that you can run the application immediately after creating it
and see a few pages. This template also includes some basic account management functions which run against the ASP.NET Membership .
2. The Intranet Application template: The Intranet Application template was added as part of
the ASP.NET MVC 3 Tools Update. It is similar to the Internet Application template,but the account management functions run against Windows accounts rather than the ASP.NET Membership system.
3. The Basic template: This template is pretty minimal. It still has the basic folders, CSS, and
MVC application infrastructure in place, but no more. Running an application created using
the Empty template just gives you an error message.
Why use Basic template? The Basic template is intended for experienced MVC developers
who want to set up and configure things exactly how they want them.
4.The Empty template: The Basic template used to be called the Empty template, but developers complained that it wasn’t quite empty enough. With MVC 4, the previous Empty
template was renamed Basic, and the new Empty template is about as empty as we can get.
It has the assemblies and basic folder structure in place, but that’s about it.
5. The Mobile Application template: The Mobile Application template is preconfigured with jQuery Mobile to jump-start creating a mobile only website. It includes mobile visual themes, a touch-optimized UI, and support for Ajax navigation.
6. The Web API template: ASP.NET Web API is a framework for creating HTTP services.
The Web API template is similar to the Internet Application template but is streamlined for Web API development. For instance, there is no user account management functionality, as Web API account management is often signify-cantly different from standard MVC account management. Web API functionality is also available in the other MVC project templates, and even in non-MVC project types.
What are the default Top level directories created when adding MVC4 application?
Default Top level Directories are:
DIRECTORY           PURPOSE
/Controllers            To put Controller classes that handle URL requests
/Models                 To put classes that represent and manipulate data and business objects
/Views                   To put UI template files that are responsible for rendering output like HTML.
/Scripts                  To put JavaScript library files and scripts (.js)
/Images                  To put images used in your site
/Content                 To put CSS and other site content, other than scripts and images
/Filters                    To put filter code.
/App_Data             To store data files you want to read/write
/App_Start             To put configuration code for features like Routing, Bundling, Web API.
What is namespace of asp.net mvc?
ASP.NET MVC namespaces as well as classes are located in assembly System.Web.Mvc.
Note: Some of the content has been taken from various books/articles.
What is System.Web.Mvc namespace?
This namespace contains classes and interfaces that support the MVC pattern for ASP.NET Web applications. This namespace includes classes that represent controllers, controller
factories, action results, views, partial views, and model binders.
What is System.Web.Mvc.Ajax namespace?
System.Web.Mvc.Ajax namespace contains classes that supports Ajax scripting in an ASP.NET MVC application. The namespace includes support for Ajax scripts and Ajax option settings as well.
What is System.Web.Mvc.Async namespace?
System.Web.Mvc.Async namespace contains classes and interfaces that support asynchronous actions in an ASP.NET MVC application.
What is System.Web.Mvc.Html namespace?
System.Web.Mvc.Html namespace  contains classes that help render HTML controls in an MVC application. This namespace includes classes that support forms, input controls, links, partial views, and validation.
What is ViewData, ViewBag and TempData?
MVC provides us ViewData, ViewBag and TempData for passing data from controller, view and in next requests as well. ViewData and ViewBag are similar to some extent but TempData performs additional roles.
What are the roles and similarities between ViewData and ViewBag?
  • Maintains data when move from controller to view.
  • Passes data from controller to respective view.
  • Their value becomes null when any redirection occurs, because their role is to provide a way to communicate between controllers and views. It’s a communication mechanism within the server call.
What are the differences between ViewData and ViewBag?(taken from a blog)
  • ViewData is a dictionary of objects that is derived from ViewDataDictionary class and accessible using strings as keys.
  • ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0.
  • ViewData requires typecasting for complex data type and check for null values to avoid error.
  • ViewBag doesn’t require typecasting for complex data type.
NOTE Although there might not be a technical advantage to choosing one format over the other, there are some critical differences to be aware of between the two syntaxes.
One obvious difference is that ViewBag works only when the key being accessed is a valid C# identifier. For example, if you place a value in ViewData[“KeyWith Spaces”], you can’t access that value using ViewBag because the codewon’t compile.
Another key issue to be aware of is that dynamic values cannot be passed in as parameters to extension methods. The C# compiler must know the real type of every parameter at compile time in order for it to choose the correct extension method.
If any parameter is dynamic, compilation will fail. For example, this code will always fail: @Html.TextBox(“name”, ViewBag.Name). To work around this,either use ViewData[“Name”] or cast the value to a specifi c type: (string) ViewBag.Name.
What is TempData?
TempData is a dictionary derived from the TempDataDictionary class and stored in short lives session. It is a string key and object value.
It keep the information for the time of an HTTP Request. This means only from one page to another. It helps to maintain data when we move from one controller to another controller or from one action to other action. In other words, when we redirect Tempdata helps to maintain data between those redirects. It internally uses session variables. Temp data use during the current and subsequent request only means it is use when we are sure that next request will be redirecting to next view. It requires typecasting for complex data type and check for null values to avoid error. Generally it is used to store only one time messages like error messages, validation messages.
How can you define a dynamic property with the help of viewbag in ASP.NET MVC?
Assign a key name with syntax,
ViewBag.[Key]=[ Value] and value using equal to operator.
For example, you need to assign list of students to the dynamic Students property
of ViewBag.
List students = new List();
countries.Add(“Akhil”);
countries.Add(“Ekta”);
ViewBag.Students = students;
//Students is a dynamic property associated with ViewBag.
Note: Some of the content has been taken from various books/articles.
What is ViewModel(taken from stackoverflow)?
First Name:</b></td>
         
.TextBoxFor(x => x.FirstName, new { maxlength = “50”, size = “50” })
              @Html.ValidationMessageFor(x => x.FirstName)
         
accepted
A view model represents data that you want to have displayed on your view/page.
Lets say that you have an Employee class that represents your employee domain model and it contains the following 4 properties:
public class Employee : IEntity
{
     public int Id { get; set; }  // Employee’s unique identifier
     public string FirstName { get; set; }  // Employee’s first name
     public string LastName { get; set; }  // Employee’s last name
     public DateTime DateCreated { get; set; }  // Date when employee was created
}
View models differ from domain models in that view models only contain the data (represented by properties) that you want to use on your view. For example, lets say that you want to add a new employee record, your view model might look like this:
public class CreateEmployeeViewModel
{
     public string FirstName { get; set; }
     public string LastName { get; set; }
}
As you can see it only contains 2 of the properties of the employee domain model. Why is this you may ask? Id might not be set from the view, it might be auto generated by the Employee table. AndDateCreated might also be set in the stored procedure or in the service layer of your application. So Id and DateCreated is not need in the view model.
When loading the view/page, the create action method in your employee controller will create an instance of this view model, populate any fields if required, and then pass this view model to the view:
public class EmployeeController : Controller
{
     private readonly IEmployeeService employeeService;
     public EmployeeController(IEmployeeService employeeService)
     {
          this.employeeService = employeeService;
     }
     public ActionResult Create()
     {
          CreateEmployeeViewModel viewModel = new CreateEmployeeViewModel();
          return View(viewModel);
     }
     public ActionResult Create(CreateEmployeeViewModel viewModel)
     {
          // Do what ever needs to be done before adding the employee to the database
     }
}
Your view might look like this (assuming you are using ASP.NET MVC3 and razor):
@model MyProject.Web.ViewModels.ProductCreateViewModel
    
         
@Html
     

     
           Last Name:</b></td>
          @Html.TextBoxFor(x => x.LastName, new { maxlength = “50”, size = “50” })
              @Html.ValidationMessageFor(x => x.LastName)
          

     

Validation would thus be done only on FirstName and LastName. Using Fluent Validation you might have validation like this:
public class CreateEmployeeViewModelValidator : AbstractValidator<CreateEmployeeViewModel>
{
     public CreateEmployeeViewModelValidator()
     {
          RuleFor(x => x.FirstName)
               .NotEmpty()
               .WithMessage(“First name required”)
               .Length(1, 50)
               .WithMessage(“First name must not be greater than 50 characters”);
          RuleFor(x => x.LastName)
               .NotEmpty()
               .WithMessage(“Last name required”)
               .Length(1, 50)
               .WithMessage(“Last name must not be greater than 50 characters”);
     }
}
The key thing to remember is that the view model only represents the data that you want use. You can imagine all the uneccessary code and validation if you have a domain model with 30 properties and you only want to update a single value. Given this scenario you would only have this one value/property in the view model and not the whole domain object.
How do you check for AJAX request with C# in MVC.NET?
The solution is independed of MVC.NET framework and is global across server side
technologies. Most modern AJAX applications utilize XmlHTTPRequest to send
async request to the server. Such requests will have distinct request header:
X-Requested-With = XMLHTTPREQUEST
MVC.NET provides helper function to check for ajax requests which internally inspects
 X-Requested-With request header to set IsAjax flag.
What are Scaffold template?
These templates use the Visual Studio T4 templating system to generate a view based on the model type selected. Scaffolding in ASP.NET MVC can generate the boilerplate code we need for create, read, update,and delete (CRUD) functionality in an application. The scaffolding templates can examine the type definition for, and then generate a controller and the controller’s associated views. The scaffolding knows how to name controllers, how to name views, what code needs to go in each component, and where to place all these pieces in the project for the application to work.
What are the types of Scaffolding Templates?
Various types are as follows,
SCAFFOLD           DESCRIPTION
Empty                  Creates empty view. Only the model type is specified using the model syntax.
Create                  Creates a view with a form for creating new instances of the model.
                             Generates a label and input field for each property of the model type.
Delete                   Creates a view with a form for deleting existing instances of the model.
                             Displays a label and the current value for each property of the model.
Details                   Creates a view that displays a label and the value for each property of the
                             model type.
Edit                       Creates a view with a form for editing existing instances of the model.
                             Generates a label and input fi eld for each property of the model type.
List                       Creates a view with a table of model instances. Generates a column
                             for each property of the model type. Make sure to pass an IEnumerable to this view from your action method.
                               The view also contains links to actions for performing the create/edit/delete                                                                                       operations.
Show an example of difference in syntax in Razor and WebForm View?
Razor @model.Message
Web Forms
Code expressions in Razor are always HTML encoded. This Web Forms syntax also automatically HTML encodes the value.
What are Code Blocks in Views?
Unlike code expressions, which are evaluated and outputted to the response, blocks of code are simply sections of code that are executed. They are useful for declaring variables that we may need to use later.
Razor
@{
int x = 123;
string y = ˝because.˝;
}
Web Forms
<%
int x = 123;
string y = “because.”;
%>
What is HelperPage.IsAjax Property?
HelperPage.IsAjax  gets a value that indicates whether Ajax is being used during the request of the Web page.
Namespace: System.Web.WebPages
Assembly: System.Web.WebPages.dll
However, same can be achieved by checking requests header directly:
Request[“X-Requested-With”] == “XmlHttpRequest”.
Explain combining text and markup in Views with the help of an example?
This example shows what intermixing text and markup looks like using Razor as compared to Web Forms:
Razor
@foreach (var item in items) {
Item @item.Name.
}
Web Forms
Item .
Explain Repository Pattern in ASP.NET MVC?
In simple terms, a repository basically works as a mediator between our business logic layer and our data access layer of the application. Sometimes, it would be troublesome to expose the data access mechanism directly to business logic layer, it may result in redundant code for accessing data for similar entities or it may result in a code that is hard to test or understand. To overcome these kinds of issues, and to write an Interface driven and test driven code to access data, we use Repository Pattern. The repository makes queries to the data source for the data, thereafter maps the data from the data source to a business entity/domain object, finally and persists the changes in the business entity to the data source. According to MSDN, a repository separates the business logic from the interactions with the underlying data source or Web service. The separation between the data and business tiers has three benefits:
  • It centralizes the data logic or Web service access logic.
  • It provides a substitution point for the unit tests.
  • It provides a flexible architecture that can be adapted as the overall design of the application evolves.
In Repository, we write our whole business logic of CRUD operations with the help of Entity Framework classes, that will not only result in meaningful test driven code but will also reduce our controller code of accessing data.
How can you call a javascript function/method on the change of Dropdown List in MVC?
Create a java-script method:
function selectedIndexChanged() {
}
Invoke the method:
x.SelectedProduct,
new SelectList(Model.Users, “Value”, “Text”),
“Please Select a User”, new { id = “ddlUsers”,
onchange=”selectedIndexChanged()” })%>
Explain Routing in MVC?
A route is a URL pattern that is mapped to a handler. The handler can be a physical
file, such as an .aspx file in a Web Forms application. Routing module is responsible for mapping incoming browser requests to particular MVC controller actions.
Routing within the ASP.NET MVC framework serves two main purposes:
  •       It matches incoming requests that would not otherwise match a file on the file system and maps the requests to a controller action.
  •       It constructs outgoing URLs that correspond to controller actions.

How route table is created in ASP.NET MVC?
When an MVC application first starts, the Application_Start() method in global.asax is called. This method, calls the RegisterRoutes() method. The RegisterRoutes() method creates the route table for MVC application.
What are Layouts in ASP.NET MVC Razor?
Layouts in Razor help maintain a consistent look and feel across multiple views within our application.As compared to Web Forms Web Forms, layouts serve the same purpose as master pages, but offer both a simpler syntax and greater flexibility.
We can use a layout to define a common template for your site (or just part of it). This template contains one or more placeholders that the other views in your application provide content for. In some ways, it’s like an abstract base class for your views.
e.g. declared at the top of view as,
 @{
       Layout = “~/Views/Shared/SiteLayout.cshtml”;
}
What is ViewStart?
For group of views that all use the same layout, this can get a bit redundant and harder to maintain.
The _ViewStart.cshtml page can be used to remove this redundancy. The code within this file
is executed before the code in any view placed in the same directory. This fi le is also recursively applied to any view within a subdirectory.
When we create a default ASP.NET MVC project, we find there is already a _ViewStart
.cshtml fi le in the Views directory. It specifi es a default layout:
@{
Layout = “~/Views/Shared/_Layout.cshtml”;
}
Because this code runs before any view, a view can override the Layout property and choose a different one. If a set of views shares common settings, the _ViewStart.cshtml file is a useful place to consolidate these common view settings. If any view needs to override any of the common settings, the view can set those values to another value.
Note: Some of the content has been taken from various books/articles.
What are HTML Helpers?
HTML helpers are methods we can invoke on the Html property of a view. We also have
access to URL helpers (via the Url property), and AJAX helpers (via the Ajax property). All
these helpers have the same goal: to make views easy to author. The URL helper is also available from within the controller.
Most of the helpers, particularly the HTML helpers, output HTML markup. For example, the
BeginForm helper is a helper we can use to build a robust form tag for our search
form, but without using lines and lines of code:
@using (Html.BeginForm(“Search”, “Home”, FormMethod.Get)) {
}
What is Html.ValidationSummary?
The ValidationSummary helper displays an unordered list of all validation errors in the ModelState dictionary. The Boolean parameter you are using (with a value of true) is telling the helper to exclude property-level errors. In other words, you are telling the summary to display only the errors in ModelState associated with the model itself, and exclude any errors associated with a specific model property. We will be displaying property-level errors separately.Assume you have the following code somewhere in the controller action rendering the edit view:
ModelState.AddModelError(“”, “This is all wrong!”);
ModelState.AddModelError(“Title”, “What a terrible name!”);
The first error is a model-level error, because you didn’t provide a key (or provided an empty key) to associate the error with a specifi c property. The second error you associated with the Title property, so in your view it will not display in the validation summary area (unless you remove the parameter to the helper method, or change the value to false). In this scenario, the helper renders the following HTML:

  • This is all wrong!

 

Other overloads of the ValidationSummary helper enable you to provide header text and set specific HTML attributes.
NOTE By convention, the ValidationSummary helper renders the CSS class validation-summary-errors along with any specifi c CSS classes you provide.The default MVC project template includes some styling to display these items in red, which you can change in styles.css.
What are Validation Annotations?
Data annotations are attributes you can find in System.ComponentModel.DataAnnotations
namespace.These attributes provide server-side validation, and the framework also supports client-side validation when you use one of the attributes on a model property. You can use four attributes in the DataAnnotations namespace to cover common validation scenarios,
Required, String Length, Regular Expression, Range.
What is Html.Partial?
The Partial helper renders a partial view into a string. Typically, a partial view contains reusable markup you want to render from inside multiple different views. Partial has four overloads:
public void Partial(string partialViewName);
public void Partial(string partialViewName, object model);
public void Partial(string partialViewName, ViewDataDictionary viewData);
public void Partial(string partialViewName, object model,
ViewDataDictionary viewData);
What is Html.RenderPartial?
The RenderPartial helper is similar to Partial, but RenderPartial writes directly to the response output stream instead of returning a string. For this reason, you must place RenderPartial inside a code block instead of a code expression. To illustrate, the following two lines of code render the same output to the output stream:
@{Html.RenderPartial(“AlbumDisplay “); }
@Html.Partial(“AlbumDisplay “)
If they are same then which one to use?
In general, you should prefer Partial to RenderPartial because Partial is more convenient (you don’t have to wrap the call in a code block with curly braces). However, RenderPartial may result in better performance because it writes directly to the response stream, although it would require a lot of use (either high site traffic or repeated calls in a loop) before the difference would be noticeable.
How do you return a partial view from controller?
return PartialView(options); //options could be Model or View name
What are different ways of returning a View?
There are different ways for returning/rendering a view in MVC Razor.E.g. return View(), return RedirectToAction(), return Redirect() and return RedirectToRoute().
Conclusion:
I hope we covered a lot of questions to brush-up. Since MVC is very vast now,I know we have missed a lot stuff too.The content in the question and answer form is also taken from few renowned books like Professional asp.net MVC4 from wrox, and few of the content is taken from myMVC articles posted earlier.  My upcoming articles will provide interview questions for EntityFramework too.

 

Best of Luck and Happy Coding J.

Code First Approach using Entity Framework 4.1, Inversion of Control, Unity Framework, Repository & Unit of Work Pattern and MVC3 Razor View


Download Source Code

Introduction :
In my previous article I discussed about developing a simple basic multilayered architecture for a .Net application.However there were few points that I skipped considering that the article was for beginners.When we talk about an application architecture there are certain points that need to be put into consideration before initiating,
  • Is the architecture loosely coupled?
  • Is it to be service based?
  • Where should the entities reside?
  • What should be Mode of Communication with the database?
  • Do it require design patterns? If yes,What patterns should be implemented?
  • Should it be based on Seperation of Concerns?
To answer these type of questions, .Net 4 has come up with a generic solution,making use of Entity Framework.
My effort in this article would be to put some light on building a generic multilayered architecture using Entity Framework 4.1 and MVC3 razor view engine.We’ll use inversion of control to resolve dependency of layers.The points to be covered in this article would be as follows,
  • Use of Seperation of Concerns,
  • Use of Code First approach,
  • POCO objects,
  • Repository Pattern,
  • Dependency Injection and Inversion of Control.
Architecture Overview:
I have created an architecture to explaing all the above mentioned points, and we’ll stick to this architecture till the end of article thus implementing practically our understanding.
I have created a very simple application to add student details in database, To edit it and to delete it,My first page shows list of all added student.
The arcitecture is service based, following are the components and pictorial representation (fig1) of it, we’ll discuss each component in detail,
  1. CodeFirstData layer.
  2. CodeFirstEntities layer.
  3. CodeFirstServices layer.
  4. MVC Portal layer.


    Architecture components:

    Let’s discuss each and every component of the defined architecture in detail,
    1. CodeFirstData layer :
    The data layer is the class library defining a layer which is responsible for interacting with database, contains context classes and a factory pattern implementation to interact with database.The layer contains the repository for each entity to map with database,thus making a complete ORM (Object Resource Model) solution.The class library references EntityFramework dll to implement the dbcontext classes.
    1. CodeFirstEntities layer:
    Entity layer acts as a model to MVC application,and also responsible for creation of DataBase objects when the dbset is first executed.It contains Entity classes in POCO form, having relations and data annotations(Rules/Constraints to be put on Database table/columns).
    The properties of the class results in column name in database and name osf the class in Dtaabase table.Primary key is either defined by the property named Id or “Classname[Id]”,in our case “StudentId”,this is default protocol set by entityframework to keep in mind while creating entities.Since this application is codefirest,we need to create entities first.
    1. CodeFirstServices layer:
    The layer contains services which uses repositories to fetch data from database. The interaction between Services and Repositories is kept loosely coupled thus implementing Inversion of Control using Dependency Injection.Its constructor based dependency injection and do not allow service to make direct instance of our repositories.Service layer acts as an interface between controllers and repositories,passes request of controller to repositories.
    1. MVCPortal layer:
    MVCPortal layer is our UI layer, it contains Model/ViewModels,Views and Controllers.I am not going into details of MVC as its not our primary target,I assume that you already know how to create and run MVC application,Lets have a quick revision of MVC,
      1. Model / Viewmodel:
    Model classea are responsible for holding up and manipulating data,we bind model/viewmodel classes to views to display model specific data.model classes are prepopulated by controllers to show data with the lehp of views.
      1. Views :
    Views holds up our UI templates, We have controller methods defined for every view, which populates View Design with data, and requests particular type of view to be rendered at user’s end as per requirement.
      1. Controllers :
    Web-based MVC frameworks map URLs to server code in a bit different fashion. Instead of mapping incoming URLs to html/aspx files, they instead map URLs to methods on classes. These classes are called “Controllers” and they are responsible for processing incoming HTTP requests, handling user input, retrieving and saving data, and determining the response to send back to the client (display HTML, download a file, redirect to a different URL, etc.).
    The layer makes use of Dependency injection to achieve Inversion of Control for services, thus not allowing controllers to directly acces services instances,The IOC is acheived using global.asax file using UnityFramework library of Microsoft.
    5. Dlls : I have created DLLs folder and given the output build path for every class library to that folder, for ease of access to Dll’s to add reference.Now each Dll will be created in the Dlls folder and we can access the desired Dll from the same folder. Also keep the EntityFramework,UnityConfiguration Dlls into it.
    IOC and DI :
    Dependency Injection is an important component in my application . All the services are required to be late bound with Model layer with Dependency Injection. In addition, the IoC container manages the lifetime of service objects. For example the Context object. I set lifetime type as PerThreadLifetimeManager in Unity configuration. This makes one and only one context object created in a single request and the different request has a different context object. Another thing I want to mention is ASP.NET MVC3 has its own way to provide Dependency Inject for controller via implementing DependencyResolver interface. The IoC container I used in the demo is Unity.
    Container :
    The “Container” or “IOC Container” is the main object that is used to create objects and inject dependencies into them. Whenever you want an object to be open to IoC, you have to use the container to create the instance using container.Resolve() method instead of the “new” keyword.
    IService service = unityContainer.Resolve();
    I have added following references to acheive the same,
    Microsoft.Practices.Unity
    Microsoft.Practices.Unity.Configuration
    The code for IOC is implemented in global.asax file.
    Step by Step Process to create the Application using EntityFramework Architecture :
    Application Overview :
    We’ll try to develop a simple studentDetails application with the help of discusses architecture,The application’s main module will be to Create a new student, Edit existing student,Delete existing student, and to show list of all students.Looking into a wider/generic perspective, the application performs CRUD operations on database with the help of EF .
    Note that we’ll not create databse by our own,we just write classes and defing connection configuration of our database server in web.config file, and let EntityFramework do rest of the job of creating database, managing database and Mapping database with our entities.
    Step1. Creating a solution and blank projects/seperating them logically/physically as layers :
    Our first initiative is to prepare our initial level architecture there by creating solution and adding project files to it, We create a solution named CodeFirstEntities and add three class libraries to it thus defining our three layers which are Entity,Data and Service, the names of the class libraries which i chose are CodeFirstEntities,CodeFirstData and CodeFirstServices respectively.
    Now add an MVC3 application to the solution called MvcPortal, that will act as a UI layer for our application. Refer fig2 for implementing the first step.


                                                                       ( fig2 )

    Step 2. Creating Entities :
    Add Student.cs class to CodeFirstEntities project , this class will contain the student details specific properties that will take the shape of database table and columns . The class makes use of DataAnnotation dll to put data annotations (rules/constraints) over the properties that will be reflected in database table.The constraints like max length and required parameter are provided as attributes over the properties of the class as shown in fig3 and fig4,

                                                                                ( fig3 )

                                                                             ( fig4)
    The above entities is very simple POCO (Plain Old CLR Object) class and the entity Student is decorated with validation attributes in the System.ComponentModel.DataAnnotations namespace. Now we want to use these entities for defining model objects for the Entity Framework 4. Using the Code First approach of Entity Framework, we can first define the entities by simply writing POCO classes without any coupling with any API or database library. This approach lets you focus on domain model which will enable Domain-Driven Development for applications. EF code first support is currently enabled with a separate API that is runs on top of the Entity Framework 4.
    Step 3. Creating Repositories/Contexts :
    Our next step is to create the contexts/repositories for our application and classes that will interact with the database.
    A. Create Context Class for Entity Framework :
    We have already prepared our domain model now let’s create a class in order to working with Entity Framework Code First. I have added reference to EntitFramework.dll CTP 4.1 to this class library project. We create two folders DBInteractions and EntityRepositories to segregate our classes as in fig5, we’ll come to that later, first let me explain you the context class.
                                                                (fig 5)


                                                                                   (fig 6)

    The above class CodeFirstContext in fig 6 is derived from DbContext that can connect your model classes to a database. The CodeFirstContext class is mapping our Student class to
    database tables Student use DbSet where TEntity is any POCO class. When we arerunning the application at first time, it will automatically create the database. EF code-first look for a connection string in web.config or app.config that has the same name as the dbcontext class. If it is not find any connection string with the convention, it will automatically create database in local SQL Express database by default and the name of the database will be same name as the dbcontext class. You can also define the name of database in constructor of the the dbcontext class. The model classes of Code First are working on the basis of conventions and we can also use a fluent API to refine our model. The convention for primary key is ‘Id’ or ‘Id’ as I discussed before. If primary key properties are detected with type ‘int’, ‘long’ or ‘short’, they will automatically registered as identity columns in the database by default. Primary key detection is not case sensitive. We can define our model classes with validation attributes in the System.ComponentModel.DataAnnotations namespace and it automatically enforces validation rules when a model object is updated or saved.
    I ) DBInteractions :
    B. Generic Repository for EntityFramework Code First:
    We have now created model class and dbcontext class. Now we create a generic repository pattern for data persistence with EF code first. Let’s create a generic repository to working with DbContext and DbSet as follows,The following classes will be added to DBInteractions folder for ease of understanding logic.


                            
                                                                            (fig 7)

    1. DataBase Factory:
    We have our database factory class defined as follows,


                                                                (fig 8)

                                                                     (fig 9)
    Where IDBFactory is the interface implemented by our factory class DBFactory.The factory class is inherited from Disposable class as shown below in fig 10,Responsible for releasing disposing database resources.
    (fig 10)
    1. RepositoryBase – The Generic Entity Repository base class :


      Above is the repository base class that contains all the methods to be implemented for CRUD DB operations, we can define more of our generic methods here, for now considering our application, these are eough for proper understanding of the working.

      E. Unit of Work
      The Unit of Work pattern maintains a list of objects affected by a business transaction and coordinates the writing out of changes and the resolution of concurrency problems.We create a class for handling Unit of Work pattern,
      Interface :


      Class :



      The Commit method written in of the UnitOfWork will call the commit method of our Context class and it will execute the SaveChanges method of DbContext class.

      II ) Repository :
      In this article, we will be primarily focus on the persistence against Student entity . Let’s create a repository for handling CRUD operations for Student
      using derive from a generic Repository EntityRepositoryBase.
      Repository class for Student :
      Interface :

      Class :

       

    Step 4. Creating a Service layer :
    Service Layer defines an application’s scope and its available set of operations from the perspective of interfacing client layers. It encapsulates the application’s business logic,
    controlling transactions and coordinating responses in the implementation of its operations. Controller classes should be made light and do not put much of business logic onto it. We can use
    the service layer as the business logic layer and can encapsulate the rules of the application.
    We define interfaces and corresponding student service for our application business logic,Since we are targetting CRUD operations, so the methods are quite simple in implementation,
    Interface :

     
    As we can see in abve interface the methods are to Get Student Details,List,Update and Delete Student.
    Class :
    usingSystem.Collections.Generic;
    usingCodeFirstData.DBInteractions;
    usingCodeFirstData.EntityRepositories;
    usingCodeFirstEntities;
    usingCodeFirstServices.Interfaces;
    namespaceCodeFirstServices.Services
    {
    publicclassStudentService: IStudentService
    {
    privatereadonlyIStudentRepository_studentRepository;
    privatereadonlyIUnitOfWork_unitOfWork;
    publicStudentService(IStudentRepositorystudentRepository, IUnitOfWorkunitOfWork)
    {
    this._studentRepository = studentRepository;
    this._unitOfWork = unitOfWork;
    }
    #regionIStudentService Members
    publicIEnumerable<Student> GetStudents()
    {
    varstudents = _studentRepository.GetAll();
    returnstudents;
    }
    publicStudentGetStudentById(intid)
    {
    varstudent = _studentRepository.GetById(id);
    returnstudent;
    }
    publicvoidCreateStudent(Studentstudent)
    {
    _studentRepository.Add(student);
    _unitOfWork.Commit();
    }
    publicvoidDeleteStudent(intid)
    {
    varstudent = _studentRepository.GetById(id);
    _studentRepository.Delete(student);
    _unitOfWork.Commit();
    }
    publicvoidUpdateStudent(Studentstudent)
    {
    _studentRepository.Update(student);
    _unitOfWork.Commit();
    }
    publicvoidSaveStudent()
    {
    _unitOfWork.Commit();
    }
    #endregion
    }
    }
    Class uses refernces of Repositories and Entities, and Dependency of Repositories is resolved in Constructor of the service itself.
    Step 5. The MVC Portal :
    Before we start MVC portal,Lets clear our logic for IOC and DI.I have already discussed IOC in the article.For resolving Dependency we create certain classes as discussed below, to get independent service request,
    We also create a custom lifetime manager for Unity to store container in the current HttpContext.
    publicclassHttpContextLifetimeManager : LifetimeManager, IDisposable
    {
    publicoverrideobjectGetValue()
    {
    varassemblyQualifiedName = typeof(T).AssemblyQualifiedName;
    if(assemblyQualifiedName != null)
    returnHttpContext.Current.Items[assemblyQualifiedName];
    returnnull;
    }
    publicoverridevoidRemoveValue()
    {
    varassemblyQualifiedName = typeof(T).AssemblyQualifiedName;
    if(assemblyQualifiedName != null)
    HttpContext.Current.Items.Remove(assemblyQualifiedName);
    }
    publicoverridevoidSetValue(objectnewValue)
    {
    varassemblyQualifiedName = typeof(T).AssemblyQualifiedName;
    if(assemblyQualifiedName != null)
    HttpContext.Current.Items[assemblyQualifiedName] = newValue;
    }
    publicvoidDispose()
    {
    RemoveValue();
    }
    }
    }
    We create a dependency resolver for resolving service dependency as follows,
    ASP.NET MVC 3 has introduced a new interface IControllerActivator which lets you activate controllers with custom behavior and can be use it for dependency injection purpose.The
    IControllerActivator interface is discoverable using the dependency resolver. Let’s create a custom controller activator class by deriving from IControllerActivator intreface
    usingSystem;
    usingSystem.Web.Mvc;
    namespaceCodeFirstPortal.IoC
    {
    publicclassCustomControllerActivator: IControllerActivator
    {
    IControllerIControllerActivator.Create(
    System.Web.Routing.RequestContextrequestContext,
    TypecontrollerType){
    returnDependencyResolver.Current
    .GetService(controllerType) asIController;
    }
    }
    }
    We also create a UnityController Factory and Configure contract and concrete types of unity in global.asax file.
    ASP.NET MVC 3 has also introduced a new interface IDependencyResolver which exposes two methods – GetService and GetServices.The GetService method resolves singly registered services
    that support arbitrary object creation and the GetServices resolves multiply registered services. Implementations of the IDependencyResolver interface should delegate to the underlying
    dependency injection container to provide the registered service for the requested type. When there are no registered services of the requested type, the ASP.NET MVC framework expects
    implementations of this interface to return null from GetService and to return an empty collection from GetServices. Let’s create a custom dependency resolver class by deriving from
    IDependencyResolver intreface in order to working with Unity to providing dependency injection.
    usingSystem;
    usingSystem.Web;
    usingSystem.Web.Mvc;
    usingSystem.Web.Routing;
    usingMicrosoft.Practices.Unity;
    namespaceCodeFirstPortal.IoC
    {
    publicclassUnityControllerFactory: DefaultControllerFactory
    {
    IUnityContainercontainer;
    publicUnityControllerFactory(IUnityContainercontainer)
    {
    this.container = container;
    }
    protectedoverrideIControllerGetControllerInstance(RequestContextreqContext, TypecontrollerType)
    {
    IControllercontroller;
    if(controllerType == null)
    thrownewHttpException(
    404, String.Format(
    “The controller for ‘{0}‘ could not be found”+ “or it does not implement IController.”,
    reqContext.HttpContext.Request.Path));
    if(!typeof(IController).IsAssignableFrom(controllerType))
    thrownewArgumentException(
    string.Format(
    “Requested type is not a controller: {0},
    controllerType.Name),
    “controllerType”);
    try
    {
    controller= container.Resolve(controllerType) asIController;
    }
    catch(Exceptionex)
    {
    thrownewInvalidOperationException(String.Format(
    “Error resolving the controller {0},
    controllerType.Name), ex);
    }
    returncontroller;
    }
    }
    Resolving Service Dependency :
    usingSystem;
    usingSystem.Collections.Generic;
    usingSystem.Web.Mvc;
    usingMicrosoft.Practices.Unity;
    namespaceCodeFirstPortal.IoC
    {
    publicclassUnityDependencyResolver: IDependencyResolver
    {
    IUnityContainercontainer;
    publicUnityDependencyResolver(IUnityContainercontainer)
    {
    this.container = container;
    }
    publicobjectGetService(TypeserviceType)
    {
    try
    {
    returncontainer.Resolve(serviceType);
    }
    catch
    {
    returnnull;
    }
    }
    publicIEnumerable<object> GetServices(TypeserviceType)
    {
    try
    {
    returncontainer.ResolveAll(serviceType);
    }
    catch
    {
    returnnewList<object>();
    }
    }
    }
    }
    global.asax :
    Add service project reference , entity project reference and data project reference to the portal.
    The SetResolver method of DependencyResolver class provides a registration point for dependency injection containers. In this method, we configure the UnityDependencyResolver class for
    providing dependency injection with Unity 2.0. The SetResolver method will be working with any dependency injection container.If you want to use StructureMap as the dependency injection
    container, you can create a dependency resolver class in order to working with StructureMap by deriving IDependencyResolver intreface and later you can configure this class with SetResolver
    method. The ASP.NET MVC 3 is providing a good support for working with dependency injection containers.
    usingSystem.Web.Mvc;
    usingSystem.Web.Routing;
    usingCodeFirstData.DBInteractions;
    usingCodeFirstData.EntityRepositories;
    usingCodeFirstPortal.IoC;
    usingCodeFirstServices.Interfaces;
    usingCodeFirstServices.Services;
    usingMicrosoft.Practices.Unity;
    namespaceMvcPortal
    {
    publicclassMvcApplication: System.Web.HttpApplication
    {
    publicstaticvoidRegisterGlobalFilters(GlobalFilterCollectionfilters)
    {
    filters.Add(newHandleErrorAttribute());
    }
    publicstaticvoidRegisterRoutes(RouteCollectionroutes)
    {
    routes.IgnoreRoute(“{resource}.axd/{*pathInfo}”);
    routes.MapRoute(
    “Default”, // Route name
    “{controller}/{action}/{id}”, // URL with parameters
    new{ controller = “Home”, action = “Index”, id = UrlParameter.Optional } // Parameter defaults
    );
    }
    protectedvoidApplication_Start()
    {
    AreaRegistration.RegisterAllAreas();
    RegisterGlobalFilters(GlobalFilters.Filters);
    RegisterRoutes(RouteTable.Routes);
    IUnityContainercontainer = GetUnityContainer();
    DependencyResolver.SetResolver(newUnityDependencyResolver(container));
    }
    privateIUnityContainerGetUnityContainer()
    {
    //Create UnityContainer
    IUnityContainercontainer = newUnityContainer()
    .RegisterType<IDBFactory, DBFactory>(newHttpContextLifetimeManager<IDBFactory>())
    .RegisterType<IUnitOfWork, UnitOfWork>(newHttpContextLifetimeManager<IUnitOfWork>())
    .RegisterType<IStudentService, StudentService>(newHttpContextLifetimeManager<IStudentService>())
    .RegisterType<IStudentRepository, StudentRepository>(newHttpContextLifetimeManager<IStudentRepository>());
    returncontainer;
    }
    }
    }
    To Start with MVC our first step is to define our connection string as follows in the web.config file.
    Steps to Create Controllers and Views :
    1. We start with home Controller, as it is the default controller set in global.asax to be called first.
      When the Index action of the controller is called we redirect it to our Student Controller,which straight away returns view to show listy of students if exist,since its first time we are creating the controller,it shows an empty list, the controller method of Student fetches student list from database , but first it creates the database, thus acheiving our objective.
    1. We create Student Controller, We define actions in the controller for each operation we want to perform as follows,
    usingSystem;
    usingSystem.Linq;
    usingSystem.Web.Mvc;
    usingCodeFirstEntities;
    usingCodeFirstServices.Interfaces;
    namespaceCodeFirstPortal.Controllers
    {
    publicclassStudentController: Controller
    {
    privatereadonlyIStudentService_studentService;
    publicStudentController(IStudentServicestudentService)
    {
    this._studentService = studentService;
    }
    [HttpGet]
    publicActionResultDetails(int? id)
    {
    varstudentDetails = _studentService.GetStudentById((int) id);
    if(studentDetails == null) thrownewArgumentNullException(“Not Found”);
    returnView(studentDetails);
    }
    [HttpGet]
    publicActionResultDelete(int? id)
    {
    varstudentDetails = _studentService.GetStudentById((int) id);
    if(studentDetails == null) thrownewArgumentNullException(“Not Found”);
    returnView(studentDetails);
    }
    [HttpPost]
    publicActionResultDelete(Studentstudent)
    {
    _studentService.DeleteStudent(student.StudentId);
    returnRedirectToAction(“List”, “Student”);
    }
    [HttpGet]
    publicActionResultEdit(int? id)
    {
    varstudentDetails = _studentService.GetStudentById((int) id);
    if(studentDetails == null) thrownewArgumentNullException(“Not Found”);
    returnView(studentDetails);
    }
    [HttpPost]
    publicActionResultEdit(Studentstudent)
    {
    _studentService.UpdateStudent(student);
    returnRedirectToAction(“List”, “Student”);
    }
    [HttpGet]
    publicActionResultCreate()
    {
    returnView();
    }
    [HttpPost]
    publicActionResultCreate(Studentstudent)
    {
    varstudentModel = newStudent()
    {
    Address = student.Address,
    Country = student.Country,
    Name = student.Name,
    Age = student.Age,
    Email = student.Email
    };
    _studentService.CreateStudent(studentModel);
    returnRedirectToAction(“List”, “Student”);
    }
    [HttpGet]
    publicActionResultList()
    {
    varstudents = _studentService.GetStudents();
    if(students.Any())
    {
    returnView(“List”, students);
    }
    returnView(“List”);
    }
    }
    }
    There are get and corresponding Posts for each method responsible for Data Updations. The Constructor of the controller initializes the Service,we can see it do not create direct instance.
    1. We Create Views for every Action,Its easy if we right click the controller action and create view,It automatically create a view with a Default folder named in the name of Constructor,So we can create all the views for our operations, and our solution looks like,
      4. Now we are ready with our application to be executed,keep your fingers crossed and see the magic, I have used _layout as master page to give some meaningful look and feel to my application,U can customize the same.When u run the application by pressing F5, We get redirected to the Index view of Student Controller,which shows list of students,since we are running it first time,we dont have existing list, and our application shows,



      1. No wonder , just have a look at your DataBase, My case I am using Sql Server 2008,


        I got a Database created automativcally with the name CodeFirstApp having Student Table, Now you can cross verify the table with your entity,its the same.So we have hit the target and our database is successfully created.

        1. Further Operations :
        You can now test the application and perform further CRUD operations in the application and see the DataBase getting updated.e.g. Create Student,


        after Submit by pressing Create, we get,


        therefore one student created.

        We can edit the same student by pressing edit link , we get the view,


        Likewise we can see the details of already created student,


        and delete the student will redirect to ,


        I had created 3 students in the same manner, You can create more and play with the application.

        Risk Factor : There is also a Risk Factor in implementing EntityFramework, If we do any change in the entity, like deleting,changing property,The context will drop and recreate the database, which may clearly lead to loss of your existing data.To avoid this critical situation, we code some more, we call SetInitializer method of DataBase class and set it to null in our dataBase Factory Class.

        usingSystem.Data.Entity;
        namespaceCodeFirstData.DBInteractions
        {
        publicclassDBFactory: Disposable, IDBFactory
        {
        publicDBFactory()
        {
        Database.SetInitializer<CodeFirstContext>(null);
        }
        privateCodeFirstContextdataContext;
        publicCodeFirstContextGet()
        {
        returndataContext ?? (dataContext = newCodeFirstContext());
        }
        protectedoverridevoidDisposeCore()
        {
        if(dataContext != null)
        dataContext.Dispose();
        }
        }
        }
        Database class is from namespace System.Data.Entity, whcih provides such feature.
        Conclusion :
        In this article we discussed about creating an application using EntityFramework 4.1 Code First Approach, We used Inversion of control and Dependency Injection to Resolve Dependency between layers.We used MVC 3 razor view engine as our UI and integrated the layers to acheive our objective.The application was a description of simple CRUD operations on Database.We learned how to use Repository Pattern,Unit of Work pattern and Unity Framework.You can download the codebase and further enhance/extend it according to your need.Happy Coding.

        Articles : http://www.codeproject.com/script/Articles/BlogFeedList.aspx?amid=7869570